Presently, no known apparatus has either been proposed or is in use which solves the particular problem addressed by the present invention.
As is well-known, rotary drilling rigs are used to drill boreholes into subsurface earth formations for the purpose of recovering aqueous and petroleum fluids. The borehole is drilled with a large bit, and a length of steel well casing is installed. Cement is pumped around the annulus of the casing. A slightly smaller bit that will fit inside the first string of casing is then used to drill the borehole deeper. The second, longer string of casing is lowered into the borehole and is cut off even with the top of the first string of casing. Cement is pumped around the annulus of the casing up to the surface of the earth (leaving cement between the strings of casing). This process of drilling deeper and adding successively smaller strings of casing continues until the desired depth is reached. If hydrocarbons are found, the well is produced; if no production results, the well is abandoned.
The steel well casing is expensive, and attempts to extract as much casing as possible are made, either after abandonment of the well or after production is completed. Extraction is often accomplished only after severing the well casing. A casing cutter is installed on the end of the kelly drill or drill string and lowered into the casing. The kelly is rotated to cut the casing from the inside out. While cutting casing, the kelly is maintained at a fixed elevation. Thus, the rollers which engage the six flat surfaces of the kelly, are maintained at the same location along the length of the kelly during the cutting operation. This causes the rollers to roll over and wear down the corners between the six (or four) flat surfaces along the length of the kelly, damaging the kelly.
This type of damage to the kelly is a function of how long the rollers are driven about the circumference of the kelly at the same location along its length. During normal drilling operations, the wear on the kelly caused by the rollers is uniform up and down its length. However, during cutting operations, with the rollers operating at the same location for a period of five to six hours (with only occasional and routine interruptions), damage to the corners of the kelly is almost inevitable.
Replacement of the damaged kelly is an expensive and time-consuming operation. Operations must cease until another kelly is transported to the rig and installed.
The present invention was developed to prevent wear to the kelly during cutting operations.